<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script>
  // 1. if
  var count = 3;
  if(count == 3){
    alert(count);
  }



  // 2. switch
  var num = 3;
  switch(num){
    case 1: {
      alert("星期一");
      break;
    }

    case 2: {
      alert("星期二");
      break;
    }

    case 3: {
      alert("星期三");
      break;
    }

    case 4: {
      alert("星期四");
      break;
    }

    case 5: {
      alert("星期五");
      break;
    }

    case 6: {
      alert("星期六");
      break;
    }

    case 7: {
      alert("星期日");
      break;
    }

    default: {
      alert("输入有误");
      break;
    }
  }


  // 3. for
  var sum = 0;
  for(let i = 1; i <= 100; i++){
    sum += i;
  }
  alert(sum);

  // 4. while
  var sum = 0;
  var i = 1;
  while(i <= 100){
    sum += i;
    i ++;
  }
  alert(sum);

  // 5. do...while
  var sum = 0;
  var i = 1;
  do{
    sum += i;
    i ++;
  }while(i <= 100);
  alert(sum);



</script>

</body>
</html>